The present invention relates to injection molding industry and more particularly to runnerless injection mold apparatus for injection molding silicone. The use of runnerless systems for injection molds is well known in the industry. Common silicone parts manufacturing uses a two component liquid composition matter. One component being liquid silicone and the other being the catalyst. When mixed together the composition will begin to cure into a solid. The curing process time, is reduced by subjecting the composition to heat above 100 degrees Celsius. This process is accomplished by the injection molding machine pushing the silicone composition into the runnerless system which distributes the silicone composition into heated cavities where the silicone composition is cured. This is a relatively low pressure process, because of the nature of the silicone composition expands when cured. This process actually fills the cavities to approximately 95% of cavity volume. The cured silicone composition expands the additional 5% to fill the cavity. The runnerless system is designed to distribute the silicone to the mold cavities while keeping the silicone cool, preventing premature curing of the silicone and eliminating waste. Most current silicone molds do not incorporate any runnerless system. The mold is constructed with runner passages to distribute the silicone to the cavities and the entire mold is heated to cure the silicone. The runner passages along with the parts are cured and the runner becomes waste, since once the silicone is cured it cannot be reused. With the high cost of silicone materials, there is a big cost savings using runnerless systems. Current molds being produced for liquid silicone injection molding do not have heaters designed directly into the mold cavities. They typically incorporate a heated mold plate where by the cavities are affixed. Typical mold plates are heated using electric heater rods placed in a mold plate adjacent to the cavity blocks transferring the heat to the blocks curing the silicone matter. Another method of heating the mold cavities is circulating hot oil through the mold plate, also resulting in heat transfer to the cavity blocks curing the silicone. One of challenges using these heating methods is even heat distribution. Uneven heat distribution can cause the silicone composition not to cure evenly within the cavity, resulting in part defects. Another challenge when incorporating a runnerless system into the injection mold is maintaining a high thermal separation between the cool runnerless system which is intended to keep the silicone matter from curing until it is injected into the mold cavities. and the hot cavities designed for curing the silicone matter. Current silicone runnerless systems are designed typically using cool (approximately 21 degrees Celsius) circulating water through passages in the runnerless system keeping the runnerless system cool. The runnerless system nozzle tips are designed to seal off against the cavity blocks to ensure the silicone composition does not leak into unwanted areas of the mold. This contact of the runnerless nozzle to the heated cavity block will cure the silicone composition in the runnerless nozzle which is un-desirable. Current runnerless systems on the market address these issues by designing water to circulate adjacent to the runnerless system, thus cooling the nozzle component preventing pre-mature curing of the silicone composition. This approach to cooling while it works, it requires a considerable amount of maintenance to ensure the water passages are kept clear to maintain water circulation.
Historically silicone injection molds have difficulty preventing premature curing of the silicone due to the inability to remove heat from the nozzle tip faster then the heat going in. One solution should been to remove the nozzle tip from the heated cavity block, but this approach adds complexity and maintenance to the mold apparatus and can be prone to silicone leaks.
It has been long known and proven that latent heat of vaporization is a very efficient means to move heat. The general application of this technology are heat pipes. By using heat pipe technology the efficiencies of heat transfer are dramatically improved and when incorporated into the runnerless system, premature curing of the silicone can be prevented. Heat pipe technology can be applied to the cooling side of the runnerless system as well as the heating side of the cavity blocks. Applying this technology to the runnerless system can dramatically improve cooling and heating efficiencies, keeping the uncured silicone at a consistent and uniform low temperature preventing premature curing of the silicone. The same heat pipe technology for removing the heat can also be applied for distributing the heat in the cavity blocks. Historically the cavity blocks have been heated using heater elements or circulating hot oil. Because the placements of these heating sources are not evenly spaced, the end result is hot and cold spots in the cavity block. The non-uniform heat distribution results in uneven curing of the silicone. By creating a void within the cavity block and partially filling it with a liquid composition under a vacuum and sealing the cavity, the cavity block becomes a heat pipe distributing the heat very evenly and efficiently across the entire cavity block. Incorporating the heat pipe technology directly into the cavity block results in quick and even heat transfer to the cavity block.
Another issue with current mold designs is cavity block construction has been historically made of one cavity block with several cavities residing in the one block. This approach, while function and economical adds to uneven heat distribution to the entire cavity block. This method takes additional time when changing cavity inserts, as the new inserts are cold and require time to heat up and the heat is not distributed evenly across the entire molding surface resulting in part defects.
The cavity block in current embodiment is of a modular construction lending to a very diverse cavity arrangement of having one or more cavities per block with several blocks per mold. Each block is smaller and incorporates the heat pipe technology resulting in faster heat up times and more even heat distribution.
It is therefore an object of the invention to provide uniform heating and cooling of the silicone mold apparatus
It is another object of the invention to provide a mold apparatus with annular heat pipe for cooling the runnerless nozzle.
It is another object of the invention to provide an runnerless nozzle with a guide seal in the nozzle tip for alignment and sealing of valve pin.
It is another object of the invention to provide an cavity block heated by heat pipe technology
It is another object of the invention to provide a cavity block locator to retain position of cavity block during heat expansion and contraction.
It is another object of the invention to provide cooling circuit to the runnerless nozzle annular heat pipe